Coaxial stub supports



April 24, 1956 R. B. MucHMoRE 7435422 COAXIAL STUB SUPPORTS Filed Feb. 20, 1952 2 Sheets-Sheet l 3a 52 30 .sa 56 m f@ C 80 j 9* 0` d 2 na 2.0 .afg

o INVENTOR HUBERT @Maa/MORE April 24, 1956 R, B, MUCHMORE 2,743,422

. COAXIAL STUB SUPPORTS Filed Feb. 20, 1952 2 Sheets-Sheet 2 Je INVENTOR-` CDAXIAL ST UB SUPPORTS Y Robert B. lMuchmore, 'Pacific Palisades, Calif., assignor `toSperry Rand Corporation, fa corporation voi" Altelaware f Applieanon :Fe-brummt), '1952,3sena11sa27a636 1s claims. icl. ssa- 291) `types of supports for the inner conductor, namely, .di-

electric beads spaced at intervals along -the conductor, or quarter wavelength shorted vstub sections of coaxial line. While 'bead-supported lines are ,adequate at radio frequencies, they start'to introduce appreciable ,disconf tinuities 'in the line in the ultra-high 'frequencyiange If the beads are evenly spaced .at vintervals s ucie'ntly close 'to give good support, as ,lin the conventional lbeadsupported line, Where the frequency .of .the transmitted energy is such that the *distance 'between the 'beads is of the order of half a wavelength, or lintegral ,multiple thereof, 'the mismatch and reflection introduced by ,each bead becomes additive along the line. tBeads can`be used at ultrahigh frequencies .if care is taken `toproperlly ,spacel or group the beads to rprevent the ,reected ,energy at each bead from adding in phase with energy reflected from other beads. However, such spacing or `grouping makes the bead-supported line frequency-sensitive, any variation in frequency changing 'the effective Ispacing of .the beads in terms of wavelength.

To provide a coaxial line which functions eiic'iently at `frequencies of vthe order of 1,000 'to 3 ,000 megacycles per second, theshorted coaxialline stub support is .preferred because it introduces substantially noloss at .the frequency where its length vis .exactly a quarter wavelength. Thus inthe coaxial stub support no consideration need be ,given to the spacing .of the stubsas is .necessary in the beadasuppor'ted line.

However, although there are nodielectric .losses in such stub supports, the use of the stub-supported c oax'ia'lline is likewise limited lin operating frequency range since'the input impedance of 'the 'stub rsupport vchanges with a change in operating frequency. At frequencies Idifferent from `the ldesign frequency, the "stub is noflongeraquarter wavelengthv device, and Iconsequently introduces 4a 'flow susceptance v.which shunts fthe .main :transmission line, this snorting susceptance causing standing avaveszwhich in turn reduce the power capacit-y andedieiency cf-the fline.

One method heretofore `proposed to -extend the frequency range of a stub-supported tcoaxial `line .is achieved by enlarging the lcenter .conductor of the .line for La yclistance of atquarter-wavelength fon .each side of :the `stub support unction. Such a compensated .stub .support .is described in Patent No. 2,446,982 issued August l0, i948 to R. V. Pound. Although the operating range of fre quencies is improved ,by changing .the diameter of the inner conductorin Athe region of the stub support, 'the practiclband width is still only of 'the order of 40% of the design frequency.

2,743,422 `Patented Apr. A24, 1956 It is the Ygeneral object of this invention to avoid :and overcome the foregoing and other difficulties Ain and objections ,to .the prior art practices by the provision of a compensated stub support which is characterized by ,its

low attenuation .and llow standing wavey ratio vover a greatly extended `band 'of frequencies in the ultra-high frequency band.

It is another ,object of ,this invention .to provide .a ycoaxial stubsupport which provides .a broad band operafion of the order of 100% band width at operating frequencies of the orderof 2,000 megacycles. Another object of this invention .is the provision of .a support for the inner ,conductor of a coaxial line which introduces Aminimum reiection over a broadband of frequencies and which may b e spaced ,at any desired intervals along the coaxial line.

These and other objects of the invention which will become apparentas the description proceeds are achieved by the provision of a stub-supported coaxial transmission line system comprising a main section of coaxial transmission'linehaving an inner conductor and an outericonductor, the inner conductor being supported by stub sections oi" coaxial .line oriented at right angles to the main section and having inner and outer conductors connected respectively to the inner and outer conductors of the main section, the stub sections each having a 'length equal Ato a quarter wavelength at vthe designV frequency and being short circu'ited at their free ends. A pair of open-ended "line sections each having .a length equal to a quarter wavelength at the design frequency are con-` nected in series with the inner conductor of the main section in the region of reach stub.section, the openended linegsections being vdisposed @on ,opposite sides .of the junction .of the vstub support along the 1main section. Each open-ended .line `section is spaced from 7the -junction by distance along the main `section .of a `,quarter wavelength atthe .design frequency. `In addition, the .admit-v tance of the mainsect'ion vis increased .in the region intermediate lthe .pairs of openended line sections, preferably by lincreasing ,the diameter at the innerfconductor.

l A better understanding of [the ,invention .may .be had byreference to the accompanying drawings, wherein:

Fig 1 is a cross-sectional view of the preferred form of the invention;

"Figs 2, 3, 4 and 5, `are circle diagrams used in the exv planation of the present invention; vand `Fig. 6 is a graphical pilot .of the voltagestanding wave ratio as a function of frequency of acoaxial line system employing the features of vthe present invention.

"With particular reference to the embodiment of the invention illustrated 'n -Fig- 1 .the numeral 10 ,indicates generally a coaxial ,transmission line having an inner conductor 12 and a concentric outer conductor 14. Thel inner conductor 12 is supported from the outer `conductorby means o'f a compensated T-stub support indicated generally at 16, the support incorporatingthenovel features of the present inventiongas hereinafter described.

The T-stubpsupport Vincludes a quarter wavelengtlhlong coaxial line stub section '18 terminated atone end by a shorting disc 20 which rigidly maintains the inner oonductor 22 and outer conductor 24 of lthe stub section .in concentric relationship.. `The outer conductor 2 4 of the stub Ysection "18 is joined at right angles to the outer Qonductor 14 of main coaxial line 10. The 'inner `conductor 22 of the stub S ection"-18 is joined at right angles to the midpoint of ya vhalf wavelength long "enlarged inner Lconductor section 26. It is to be understood-.that the wavelength in determining the'length ofthe stub section 1S and enlarged inner conductorsection 26 is the wavelength of 'an electromagnetic wave *in free 'space at the lcenter frequency of the band lof n,frequencies over which the T-stub support is to operate. This center frequency dis commonly referred to as the design frequency of the system.

The present invention further provides a pair of opencircuited line sections 2S and 30 which are connected in series with the inner conductor 12 of the coaxial line 10. The open-circuit line sections are effectively positioned adjacent to the ends of the enlarged inner conductor section 26.

One method of constructing the open-circuit line sections is illustrated in Fig. 1, in which the ends of the enlarged conductor section 26 are each provided with an axially extending bore 32 into which is inserted a reduced diameter portion 34 of the adjoining end of the inner conductor 12. insulating sleeves 36 made of polystyrene or other suitable dielectric material, secure the portions 34 concentrically within the bores 32 to provide a rigid mechanical coupling therebetween. Dielectric discs 38 and washers 40 are provided in each joint to insulate the enlarged inner conductor section 22 from the adjoining inner conductor 12 of the main coaxial line 10.

Thus the reduced diameter portion 34, the bore 32, and dielectric sleeve 36 combine to form an open-circuit coaxial line section in series with the inner conductor 12 on either side of the enlarged inner conductor section 26. The length of the series coaxial line sections 28 and 30 is a quarter wavelength. However, since these opencircuited line sections are dielectric filled, the wavelength used in calculating the length of these sections is based on the wavelength of an electromagnetic wave in the din electric medium at the design frequency, the relationship between the wavelength ko in free space to the wavelength M in the dielectriclled line being given by the equation arman/i;

where ,e is the dielectriconstant. The wavelength for a polystyrene-filled coaxial line is approximately 0.6 the wavelength in free space while the wavelength of an airlled coaxial line is equal to the wavelength in free space. Because the quarter wavelength dielectric-filled opencircuit line sections are thus physically shorter than a quarter wavelength coaxial line section filled with air, the open-circuit line sections canbe effectively folded within the half wavelength long enlarged inner conductor section 26 to provide a compact and structurally rugged support.

By way of illustration, a physically practical stub support incorporating the features above described which provides a theoretical band width of better than 100% of the design frequency has the following properties:

With a main coaxial line section having a characteristic impedance of 70 ohms, the section of the coaxial line embodying the enlarged inner conductor section 26 is designed to have a characteristic impedance of 50 ohms,

the coaxial line stub is designed to have a characteristic impedance of 45 ohms, and the open-circuit line sections are each designed to have a characteristic impedance of 27.5 ohms. While a T-stub support having these characteristic impedances for the various components of the support does not necessarily represent the optimum which may be achieved in a broad band support incorporating the features of the invention, it does represent a physically practical support which can be readily constructed and which gives more than twice the band width heretofore achieved using the shorted T-stub supports with half wavelength transformers.

The operation of the T-stub support described above may be more clearly understood through the study of impedance circle diagrams as shown in Figures 2, 3, 4 and 5. Such circle diagrams are widely used for simple graphical analysis of transmission line behavior. The complete detailed description ofthe nature and use of such diagrams may be found on pages 22 through 33 of the book Microwave Transmission of J. C. Slater, first lli edition i942, McGraw Hill Book Company, New York and on pages 689 through 693 of an article entitled Graphical Solution of Voltage and Current Distribution and Impedance of Transmission Lines by R. C. Paine, in the Proceeding of the Institute of Radio Engineers, volume 32, November, 1944. Since the use of the impedance circle diagram is so well established, a repetition of the full description is believed to be unnecessary.

The circle diagram is employed here to show the change in impedance of the load produced by the transmission line section in the region of the support 16 with respect to the electrical length of the section to ascertain how the load produced by the support matches the charactcristie impedance of the main coaxial line 10 at frequencies other than the design frequency. It will be appreciated that at the design frequency, the stub 18 introduces no shunting susceptance, the enlarged conductor section 26 being exactly half a wavelength long introduces no reflections, and the open-circuit line sections have zero impedance, so that a perfect match between the support and the line is achieved.

The circle diagram of Figure 2 is a plot of the load im pedance of the support at a frequency of .6 of the design frequency. In the circle diagram the reactance is plotted along the ordinate axis and resistance is plotted along the abscissa axis, both the reactance and resistance being normalized with respect to the characteristic impedance of the transmission line whose characteristics are to be investigated. Superimposed on the rectangular coordinate graph there is a first series of circles having centers on the ordinate axis, each of these circles intersecting the abscissa axis at the point (l, 0) and representing a Vconstant electrical distance, ,81 in degrees, along the transmission line.` Portions of two such constant i circles are shown at 42 and 44.

A second series of circles, having centers'on the abscissa axis, are provided which are mutually orthogonal with the first series of circles and which surround the point (1, O) on the abscissa axis. Each of these second series of circles intersects the abscissa axis at mutually recipro cal points, thus forming a family of eccentric circles. Two such circles are shown at 46 and 48 by way of illustration.

The significance of the family of eccentric circles is as follows: If the point (l, 0) is taken to represent the normalized characteristic impedance of any transmission line and the line is terminated by a load impedance which is different than the characteristic impedance of the line, the input impedance of the line at any arbitrary point on the line will fall somewhere on the particular eccentric circle passing through the point on the rectangular coordinate graph corresponding to the normalized load impedance.

The impedance along the transmission line in the region of one of the supports of the present invention, where the frequency is .6 of the design frequency for example, may be plotted by starting at the point a at which point the impedance is that of the characteristic impedance of the transmission line, which is 70 ohms in the present illustrative example. The characteristic impedance of the transmission line, which for the convenience of plotting is normalized with respect to the 50 ohm characteristic impedance of the enlarged conductor section 26 of thc sup port, therefore 1.4, which is plotted at point a (1.4, 0) on the circle diagram of Figure 2.

The impedance of the open-circuit line section 28, which is in series with the transmission line at a point a, is next added to the impedance of the line as the impcdance is plotted moving along the section of the line in the region of the support. The open-circuit line section 28 has a normalized capacitive reactance of .4, which, when added to the impedance of the line, brings thc plot on the chart of Figure 2 to a point b, whose coordinates are (1.4, 0.4).

ilhe :combined ,impedance .of the dine and `the .opemcirenit 'line section is transformed fa'long dhe enlarged com doctor. section 26 to :the T-fstub junction, which fon the chart brings the .plot .to the point c by following the appropriate eccentric .circle 46 fpassingithrough the point fb through 1an arc of extent corresponding to t6 of a quarter wavelength, 'or 54, proceeding fin vthe `clockwise direc-Vv the admittance at point d which brings .the .plot to point e.

inverting the admittance at Ipoint e backl to the corresponding 4impedance value by following .the 1eccentric circle 46 passing throughr the lpoint 'e aFdis-tance of 9G electrical degrees on the chart brings'jthe plot to the point f. Further translation vclockwise Jalong this circle a distance of 54 electrical 'degrees on thee-hart, transforms the impedance at the point e along the enlarged inner conductor section 26 to the `point where 4the opencircuit Aline section 30 is positioned, whichbrings the plot to the point g. Addition ofthe impedance of the open-circuit line section 30 completes ythe plot to the point h.y In the plot of Fig. '2, 'the linesa'b, de, and lg-h actually are coincident 'but have been 'separated slightly to present a clearer picture lo f 'the mannerv in' whichthe graph is plotted.

It will be noted that the `point a and *point Ih yare the same and that in following varound the "ploto'f the im-y pedance of the ,transmission line'sectionfroni onel'end of the T-stub support to the other that the plot completely c'loses, which means that .the input impedance `of vthe line looking in at the leftend ofthe T-stub support is identical to the impedance' of the line looking to 'the right from the other end of the T-:stub support, `and that.

there is 'a perfect .match'of ,the T-s'tub support to thc transmission line at .6 of .the design frequency.

lPig. 3 'is a plot similar to Fig. 2 of 'the impedance of the load produced Vby the `,transmission :line section in the region of the support lat a frequency vof ,L8 of the design frequency. it will be .noted ithat at this 'intermediate frequency the point h representing 'the input impedane does 4not quite fall back on ,thopoin't a, which indicates that the 'impedance o f the line at one end of the T-stub support does not match exactly .the impedance of the jline at the other end of the T-,stub Support .looking in the `same direction. However, vthe ,mismatch at this intermediate [frequency is relatively small ,and ,pro-V (luces a VSWR which is wellwithin practical'deslgn y limits. i Y

Fig. 4 yis* asimilar plot at a .frequency of l.5 the design frequency, again showing that the .impedance of fthe T- stub lsupport substantially matches .the characteristic impedance of the line, as indicated .by the Iclose proximityof the .points a and h.

. struction.

.d 'ond opcnacircuit line :section iis y.added fto .complete .the plot to point The similarity :between Figs. 4 .and 5 is believed evident, Fig. 5 Iizeing .substantially identical to Fig. 4 inverted `about .the fabscissa axis.

A plot of VSWR, .which .is Aa imeasure of `the `absolute magnitude of mismatch between the .points a and h at any given frequency, as a function of frequency is shown in .'Fig. V6. On a linear scale of frequency, ythe rcurve of Fig. :6 is symmetrical about .the design frequency. The ydotted line curve `of Fig. 6 is a vplot on the same scale of the prior art stub support having a half wavelength transformer in series with the inner conductor -at the point of the stub. The resulting band -width over which substantial match of the T-stub support -to the line is achieved thus extends atleast from the .5 to 1.5 of the design frequency, orv a band width -of at -least which represents a considerable improvement over the band Width vof vheretofore known T-stub Isupports -for coaxial lines. s Fromthe above-description itrwill be recognized that the objects of the invention are met lby the provision of .a support lfor the inner conductor of a coaxial transmission linehaving a broad band operation which'is-more than double the best results of the prior art practice in the use of compensated stubs. Furthermore the stub support of the present 'invention can be used in a 'line for transmitting frequencies in a range in which dielectric bead-supported lines become inecient and frequency-sensitive.

While conceivably the compensating series impedance ofthe T -stub support or" the present vinvention may be physically incorporated in other ways, as by folding the open-circuit line sections outwardly along the conductor instead of inwardly 4toward the junction with the stub section, `the preferred form illustrated provides a mechanically rugged and practical stub `supported con- Also the description ofthe invention has been in terms of a support for a coaxial line, 'but `the invenf tion may equally well be considered as a lter 'having broad band-*pass properties, in which case,. the Asupport feature no longer being essential, the principles of the.

invention may ,be applied to parallel twowire 'line systems Vas well as coaxial 'line systems.

Since many changes could be made in thea'bove construction and many apparently widely different .embodi' ments of this invention could 'be made without departing from the scope thereof, it is intended that all matter contained in the above .description or shown in the ;a c.

companying drawings shall be interpreted as illustra tive 'and not in a limiting .sense` 'What is' claimed is:

l. A stub-supported transmission line comprising a main .section of coaxial transmission line having .an Vin- The Lgraph-ical plot of Fig. .5 .is similar .te that' .of rig.

2 .but at sa frequency .of f1.5 .times the .design .frequency It will be noted that .the vteactance ofthe open-circuit line .sections is inductive so `that point ...b .is above the abscissa axis. As before the impedance at point Vb is transformed in a clockwise ,direction along Van eccentric` circle a distance of 1.5 times a quarter wavelength, qor .electrical degrees on ythe ichart, .to a point ,c :and/invetted to the r.point d. The .inductive susceplalloe of the stub is then `added -to .bring the plot to point e. Again inverting back to impedance brings the graphical plot to point f and transforming through 13,5" :brings the plot to point .g where .the .inductive reactance of the secner conductor and .anrouter conductor adapted to transmit frequencies higher and lower thanta design (frequency, a vstub section of coaxial transmission line having ,an inner and outer conductor connected respectively to `the inner .and outer conductorsv of the main .section in substantially perpendicular relationship, the stub section having ,an electrical length ofV substantially a quarter.

wavelength at the design frequency and being shorted at its vfree end, ,the inner conductor of the main .section having .an enlarged diameter portion adjacent the point of junction with .the .inner conductor of the .stub section and extending an electrical distance ofa yquarter iwave-` length .at the .design frequency .in'both directions from said junction, a pair -of open-circuit line sections connected in Series with .the main .section and spaced apar-t at .their series .connection points by. an electrical distance of half a wavelength at `the design frequency, tthe openacircuit line sections including reduced 'diameter portions on the inner conductor of the main section concentrically extending .into :a bore in each end .of fthe eulangled diameter portion, and vsleeves of insulating ma 7 terial between the bores and reduced diameter portions for securing the adjacent inner conductor portionsl in open-circuit relationship, the open-circuit line sections having an electrical length of substantially a quarter wavelength at the design frequency.

2. A stub-supported transmission line comprising a main section of coaxial line having inner and outer conductors adapted to transmit frequencies higher and lower than a design frequency, a stub section of coaxial transmission line having inner and outer conductors connected respectively to the inner and outer conductors of the main section in substantially perpendicular relationship, the `stub section having an electrical length of substantially a quarter wavelength at the design frequency and being shorted at its free end, the inner conductor of the main section having an enlarged diameter portion adjacent the point of junction with the inner conductor `of the stub section and extending an electrical distance of a quarter wavelength at the design frequency in both directions from said junction, and a pair of open-circuit line sections connected in series with the inner conductor of the main section of coaxial transmission line adjacent the ends of the enlarged diameter portion, each open-circuit line section having an electrical length of substantially a quarter wavelength at the design frequency.

3. A stub-supported transmission line comprising a main section of coaxial transmission line having inner and outer conductors adapted to transmit frequencies higher and lower than a design frequency, a stub-section of coaxial transmission line having inner and outer conductors connected respectively to the inner and outer conductors of the main section in substantially perpendicular relationship, the stub section having an electrical length of substantially a quarter wavelength at the design frequency and being shorted at its free end, the inner conductor of the main section having an enlarged diameter portion adjacent the point of junction with the inner conductor of the stub section and extending an electrical distance of a'quarter wavelength at the design frequency in both directions from said junction, and a pair of opencircuit line sections connected in series with the main section, said sections having their series connectionV points with said main section respectively positioned on either side of said junction by an electrical distance of a quarter wavelength at the design frequency, each open-circuit line section having an electrical length of substantially a quarter wavelength at the design frequency.

4. A stub-supported transmission line comprising a main section of coaxial transmission line having inner and outer conductors adapted to transmit frequencies higher and lower than a design frequency, a stub section of coaxial transmission line having inner and outer conduc tors connected respectively to the inner and outer conductors of the main section in substantially perpendicular relationship, the stub section having an electrical length of substantially a quarter wavelength at the design frequency and being shorted at its free end, and a pair of open-circuit line sections connected in series with the main section and disposed on opposite sides of the junction between the stub section and the main section, the opencircuit line sections being spaced from said junction at their series connection points by an electrical distance of a quarter wavelength at the design frequency, each opencircuit line section having an electrical length of substantially a quarter wavelength at the design frequency.

5. A stub-supported transmission line comprising a main section of coaxial transmission line having inner and outer conductors adapted to transmit frequencies higher and lower than a design frequency, a stub section of coaxial transmission line having inner and outer conductors connected respectively to the inner and outer conductors of the main section in substantially perpendicular relationship, the stub section having an electrical length of substantially a quarter wavelength at the design frequency and being shorted at its free end, and a pair of two-conductor resonant line sections, the two conductors of each resonant line section rbeing connected at the corresponding ends thereof in series with one of the conductors of said main section, the series connection points between said resonant line sections and said main section being respectively positioned at a quarter wavelength distance from and on opposite sides of the junction between the stub section and the main section, the resonant line sections having an electrical length of substantially a quarter wavelength at the design frequency.

6. A coaxial transmission line system comprising a main coaxial line section, a short-circuited coaxial line section connected in shunt with the main line section, a pair of open-ended coaxial line sections connected in series with one of the conductors of the main line section respectively on each side of the junction of the short-circuited line section and main line section at an electrical distance of Y a quarter wavelength at the design frequency of the line,

the short-circuited and open-circuited coaxial line sections having an electrical length of a quarter wavelength at the design frequency, and means for increasing the characteristic admittance of the main line section in the region intermediate the junctions of the open-ended line sections and the main line section.

7. Acoaxial transmission line system comprising a main coaxial line section, a short-circuited coaxial line section connected in shunt with the main line section, and a pair of open-ended coaxial line sections in series with one of the conductors of the main line section connected respectively on each side of the junction of the shortcircuited line section and main line section at an electrical distance of a quarter wavelength at the design frequency of the line, the short-circuited and open-circuited coaxial line sections having an electrical length of a quarter wave- 1 length at thedesgn frequency.

. length of a quarter Wavelength at the design frequency,

a pair of resonant line sections in series with one of the conductors of the main line sections connected respectively on each side of the junction of the short-circuited line section and main line section at an electrical distance of a quarter wavelength at the design frequency of the line, and means increasing the admittance of the main line section in the region intermediate the junctions of the resonant line sections and the main line section.

9. A coaxial line system for ultra high frequency energy comprising a main section of coaxial transmission line having an inner and an outer conductor, a short-circuit stub section of coaxial transmission line having an inner and an outer conductor connected at one end respectively to the inner and the outer conductor of the main section and connected together at their opposite ends, and a pair of open-circuit stub sections of coaxial transmission line each connected at one end thereof in series with one of the conductors of the main section of transmission line, the points of series connection of the open-circuit stub sections being displaced in opposite directions along the main section from the point of junction with the shortcircuit stub section, the physical lengths of the shortcircuit stub section, the open-circuit stub sections, and the line sections between the connecting point of the shortcircuit stub section and respective open-circuit stub sections all being related to each other in inverse proportions to the square roots of the dielectric constants of the respective coaxial line sections, the characteristic impedance of the portion of the main section of coaxial transmission line between the points of series connection of the open-circuit stub sections being appreciably lower than the remaining portions of the main sections.

10. A coaxial line system for ultra high frequency energy comprising a main section of coaxial transmission line having an inner and an outer conductor, a shortcircuit stub section of coaxial transmission line having an inner and an outer conductor connected at one end respectively to the inner and the outer conductor of the main section and connected together at their opposite ends, and a pair of open-circuit stub sections of coaxial transmission line each connected at one end thereof in series with one of the conductors of the main section of transmission line, the points of series connection of the opencircuit stub sections being displaced in opposite directions along the main section from the point of junction with the short-circuit stub section, the physical lengths of the short-circuit stub section, the open-circuit stub sections, and the line sections between the connecting points of the short-circuit stub section and respective open-circuit stub sections all being related to each other in inverse proportion to the square roots of the dielectric constants of the respective coaxial line sections.

11. A two-conductor line system comprisingv a main section of two-conductor transmission line, a short-circuit stub section of two-conductor transmission line connected at one end across the main section of transmission line and being shorted at the other end, and a pair of opencircuit stub sections of two-conductor transmission line each connected at one end thereof in series with one of the conductors of the main section of transmission line, the points of series connection of the open-circuit stub sections being displaced in opposite directions along the main section from the point of junction with the shortcircuit stub section, the physical lengths of the shortcircuit stub section, the open-circuit stub sections, and the line sections between the connecting point of the shortcircuit stub section and respective open-circuit stub sections all being related to each other in inverse proportion to the square roots of the dielectric constants of the respective line sections.

12. A coaxial transmission line System comprising a main coaxial line section having inner and outer conductors, a short-circuit coaxial line section connected in shunt with the main line section, the short-circuit line section having an electrical length of a quarter wavelength at the design frequency7 and a pair of two-conductor resonant line sections, one of the conductors of the main section having an intermediate portion adjacent the junction with the short-circuit line section and insulated from the rest of the main section at points a quarter wavelength on either side of said junction, the two conductors of each of the resonant line sections beingA connected at their corresponding ends to said one conductor of the main section on either side of said insulated points, whereby the resonant line sections are series connectedy between said insulated portion and the rest of said one conductor of the main section.

section, the series connection points between the respective resonant line sections and Ysaid one conductor of the main section being positioned respectively Von each side of the junction of the short-circuit line section and the main line section.

14. A two-conductor line system comprising a main section of two-conductor'transmission line, a rst resonant two-conductor line section having adjacent ends of the two conductors connected in shunt across the two conductors of the main section, Ysecond and third resonant two-conductor line sections having adjacent ends of the two conductors connected in series with one of the two conductors ofthe main section, the series junction points between the main section and said second and third resonant line sections being respectively positioned a quarter wavelength on either side of the junction of the main section with the first resonant line section.

15. A stub-supported transmission line comprising a main section of coaxial line having inner and outer conductors adapted to transmit frequencies higher and lower than a design frequency, a stub section of coaxial transmission line having inner and outer conductors connected respectively to the inner and outer conductors of the main section in substantially perpendicular relationship, the stub section being shorted at its free end, Vthe inner conductor of the main section having an enlarged diameter portion adjacent the point of junction with the inner conductor of the stub section, and a pair of open-circuit line sections connected in series with the inner conductor of the main section of coaxial transmission line adjacent the ends of the enlarged diameter portion, the physical lengths of the short-circuited stub section, the open-circuited stub sections, and the line sections between the short-circuited stub section and the respective open-circuit stub sections being related to each other in inverse proportions to the square roots of the dielectric constants associated with the respective sections.

References Cited in the file of this patent UNITED STATES PATENTS 2,195,717 

